如何在“func applicationWillResignActive”中访问UIViewController的变量？ Swift，iOS xcode

Question

我的UIViewController类设置如下：

class ViewController: UIViewController {

    var currentTask: NSURLSessionTask?

    ...

}

如果用户按下主页按钮，我想

self.currentTask.cancel()

但是如何从AppDelegate.swift访问这个变量？

func applicationWillResignActive(application: UIApplication) {

}

Answer 1

在UIViewController类中的viewDidLoad（）中，添加

    // Add UIApplicationWillResignActiveNotification observer
    NSNotificationCenter.defaultCenter().addObserver(
        self,
        selector: "resigningActive",
        name: UIApplicationWillResignActiveNotification,
        object: nil
    )
    NSNotificationCenter.defaultCenter().addObserver(
        self,
        selector: "becomeActive",
        name: UIApplicationDidBecomeActiveNotification,
        object: nil
    )

对于Swift 4，iOS 11，请使用：

 NotificationCenter.default.addObserver(
    self, 
    selector: #selector(ViewController.resigningActive), 
    name: NSNotification.Name.UIApplicationWillResignActive, 
    object: nil)

 NotificationCenter.default.addObserver(
    self, 
    selector: #selector(ViewController.becomeActive), 
    name: NSNotification.Name.UIApplicationDidBecomeActive, 
    object: nil)

最后将这两个函数添加到视图控制器中：

@objc fileprivate func resigningActive() {
    print("== resigningActive ==")
}

@objc fileprivate func becomeActive() {
    print("== becomeActive ==")
}

Answer 2

对于Swift 4及更高版本，您可以使用

UIApplication.willResignActiveNotification

和

UIApplication.didBecomeActiveNotification

通知名称。